Field of the Invention
The present invention comprises a patient positioning device, a medical imaging system, and a method for medical imaging.
Description of the Prior Art
In the case of medical needle interventions, such as biopsies, for example, fine needle biopsy, abbreviated FNAB (Fine-needle aspiration biopsy), for acquiring cells from internal organs in diagnoses pertaining to a suspected tumor, or with catheter ablations, image-based navigation support or trajectory planning plays an increasingly important role. In order to depict the structure of tissues and organs in the body of a patient and/or for the spatial imaging thereof, imaging using magnetic resonance tomography (MRT) is an option. A disadvantage with the use of a magnetic resonance tomography apparatus, or a computed tomography (CT) apparatus, the mechanical structure thereof, in which a patient must be conveyed into a tunnel-like opening of the apparatus. It is not possible for a physician to operate in this space. Furthermore, MRT or CT imaging is not possible, or is only possible to a limited extent, due to image artifacts caused by the interaction of the strong static or dynamic electromagnetic fields with the instruments used in a needle intervention, which are generally metallic. For this reason, needle interventions, have conventionally been carried out without MRT or CT imaging, and instead are navigated either without image-based navigation support, i.e. “blind,” or modalities are used such as ultrasound or conventional X-ray imaging that, although they do not exhibit the aforementioned disadvantages, depict tissues and organs with lower contrast. Moreover, in the case of X-ray imaging, the patient is subjected to X-ray radiation. Other possibilities for supporting the navigation of a medical needle instrument are markers, positioning aids, camera-based navigation systems and laser systems, which, due to the lack of real-time depiction of the instrument during the intervention, can be used only to a limited extent. Attempts to optimize the mechanical structure of CT or MRT apparatuses, such as by means of a shorter or wider gantry, are only possible to a limited degree, and do not solve the main problem.
A promising approach is the use of a multimodal imaging, in which two or more medical imaging modalities are used. As a result, the advantages and strengths of the respective imaging processes can be combined. Systems are known in which a projection of a spatial image is superimposed over a live screening image, in order to superimpose a representation of tissues having a stronger contrast onto a current image of a medical instrument. Another method is described in the publication by C. Weiss et al., MR-US Fusion for Targeted Prostrate Biopsy, 2010 ISMRM (International Society for Magnetic Resonance in Medicine), Annual Meeting, May 1-7, 2010, Stockholm, Sweden. As described herein, a previously acquired MRT image of a volume that includes the prostate of a patient is superimposed on a spatial real-time ultrasound image. The superimposing, or fusing, is achieved using data describing the spatial position of the ultrasound head of the ultrasound apparatus, which are acquired using a position detection system, referred to as a “tracking system”. A problem with this method is that when the position of the patient changes after the MRT imaging, it is then difficult, or no longer possible, to fuse the images. This problem arises in particular when the patient is repositioned between the MRT imaging and the ultrasound imaging, or because of movements by the patient, if the ultrasound images are made much later than the MRT images.